Permanent Colours of Opake Bodies. 259 



the great difrerence of their denfity, with refpedt 

 to that of the metal, vividly refled a white light. 



The rough furfaces of metals confift of minute 

 irregular prominences, and cavities, from which 

 the rays are refleded, in different direftions, 

 whereby they are blended and intermixed, and, 

 by their mixture, conftitute whitenefs. 



But, the polifhed furfaces of metallic mirrours 

 equably, and regularly, refledt the feveral incident 

 rays, according to their feveral angles of incidence: 

 fo that the reflefted rays do not interefere with 

 each other, but remain feparate and unmixed, and 

 therefore diRinclly exhibit their feveral colours. 



From hence it is evident, that white furfaces 

 "cannot adt upon the light, as mirrours : becaufe 

 all the rays, which are refle(5ted from them, are 

 promifcuoufly, and diforderly blended. 



Nor can the furfaces of mirrours appear white, 

 except when white objeds are cafually oppofed 

 to them : becaufe the rays which fall upon them 

 from coloured objedts, are refleded feparately, 

 and diftinclly, whereby colours are exhibited. 



In forming ornamental works of filver, artifls 

 fometimes avail themfelvesofthecontraft, between 

 the refplendent whitenefs of the unpoliilied parts 

 of the metal, and the regular refledions which 

 are difplayed by its polifhed parts. 



White metals are peculiarly adapted to the 

 formation of mirrours, as their furfaces are capable 

 of being polifhed, by which they are qualified 



S 2 equably. 



